ToME: the Tales of Maj'Eyal

So when I took it straight away, it gave me negative 10 fortress energy.

I think this is more of a convenience than a bug. It takes long enough to get to the fortress, it would just be annoying to then have to leave (if you have nothing to transmo) get some loot, transmog it, and come back.

It says it costs 10 energy, and it does, you just don't have to have it at the time.

Even if it was unintentional, I wouldn't recommend changing it at this point.

It really seams to serve no purpose. Why not remove the energy cost at all?

Maybe it could be free. And maybe also you could have it reapplied for free if it is removed by a sustain remover.